This invention relates in general to the manufacture of vehicle wheels and in particular to a process for spin forming a portion of a vehicle wheel rim.
It is known in the art to manufacture a one piece vehicle wheel. Referring to the drawings, there is shown in FIG. 1 a fragmentary sectional view of a typical prior art one piece wheel 10. The wheel 10 has a circular wheel disc 11 which extends across an annular wheel rim 12.
The wheel disc 11 includes a wheel hub 15 having a central pilot hole 16 and a plurality of wheel lug holes 17 (one shown) formed therethrough. The hub 15 is supported by a plurality of wheel spokes 18 (one shown) within an annular sidewall 20 which forms the outboard end of the wheel rim 12.
The wheel rim 12 includes an outboard tire bead retaining flange 21 which extends in a radial outward direction from the sidewall 20. The rim 12 further includes an outboard tire bead seat 22 which is formed in the sidewall 20 adjacent to the retaining flange 21. The rim 12 also includes an outboard tire safety bead 23 formed in the sidewall 20 between the tire bead seat 22 and a deep well 24. A leg portion 25 extends axially across the rim 12 from the deep well 24 to an inboard tire safety bead 26. An inboard tire bead seat 27 is formed adjacent to the safety bead 26. The inboard end of the wheel rim 12 terminates in a conventional inboard tire bead retaining flange 28.
Referring to FIG. 2, there is shown a flow chart for a known manufacturing process for fabricating the one piece wheel 10 illustrated in FIG. 1. In functional block 30, a wheel blank is formed from a light weight metal or light weight metal alloy by a conventional process, such as gravity, low pressure or die casting, or forging. The wheel blank includes a wheel rim formed integrally with a wheel disc and is formed oversize having the approximate shape of the wheel.
Finishing the wheel blank typically includes multiple machining operations. If the wheel blank is cast, sawing machines remove any casting gates and risers from the wheel blank in functional block 31. In functional block 32, a drilling machine drills the central pilot hole 16 and the wheel lug holes 17 through the wheel hub 15. In functional block 33, the wheel blank is mounted upon a wheel lathe for machining to its final shape. During the machining operations, the inboard surface of the wheel hub is usually faced to provide a flat mounting surface. Similarly, the outboard wheel hub surface is faced and both the inner and outer surfaces of the wheel rim are turned to their final shapes. During the turning of the wheel rim outer surface, the tire bead seats are turned to their final diameter. Alternately, the wheel blank can be mounted upon a wheel spinning machine (not shown), and the outer surface of the rim portion of the blank spun into its final shape.
Typically, the machined wheel is heat treated to assure that the wheel has desired mechanical properties, as shown in functional block 34. However, the heat treatment can cause irregularities in the circularity of the wheel rim which affect the concentricity of the tire bead seats, causing undesired vibrations when the wheel is mounted upon a vehicle and the vehicle operated. Accordingly, the wheel is usually machined following heat treatment, as shown in functional block 35 to true the concentricity of the tire bead seats. Finally, in functional block 36, portions of the wheel can be painted or covered with a clear coating to protect the wheel from corrosion and/or enhance its appearance.
It also is known in the art to fabricate a two piece vehicle wheel by attaching a wheel disc to a separately formed wheel rim. Typically, the wheel disc is cast or forged while the rim is rolled from strip stock. Such two piece wheels are less expensive to manufacture than a cast one piece wheel while permitting use of stylistic designs for the wheel disc. Both the wheel disc and rim can be formed from alloys of the same light weight metal, such as aluminum, magnesium or titanium, or, as a further cost reduction, a wheel disc formed from an alloy of a light weight metal can be attached to a rim rolled from steel. When different metals are used to form the wheel disc and wheel rim, the wheel is usually called a bimetal wheel.
To further improve the appearance of the wheel, the wheel disc can be formed to include the outboard tire bead retaining flange. The resulting wheel disc, which is called a full face wheel disc, is attached to the outboard end of a partial wheel rim. The attachment can occur at the outboard tire bead seat, the dropwell, or another location. The assembled wheel is often referred to as a full face wheel. When a tire is mounted upon a full face wheel, the joint between the wheel disc and wheel rim is completely hidden and only the wheel disc is visible. A decorative finish is often applied to the face of the wheel disc to further enhance the appearance of the wheel. Examples of typical decorative finishes include metal plating, such as chromium plating, clear coatings and paint.
Referring to FIG. 3, there is shown a flow chart for a known manufacturing process for fabricating a two piece wheel. In functional block 40 full face wheel disc is formed by a conventional process, such as casting or forging. The wheel disc is heat treated in functional block 41 and then machined to final shape in functional block 42.
While the wheel disc is being formed, a flat strip of metal is rolled into a circular hoop and the ends butt welded together in functional block 45. The hoop is formed into a partial wheel rim in functional block 46 by a conventional spinning process. The hoop is mounted upon a mandrel and the hoop and mandrel are spun while rollers are pressed against the outer surface of the hoop. The rollers and mandrel cooperate to form the hoop into a partial wheel rim.
In functional block 47, the partial wheel rim is attached to the wheel disc formed in functional blocks 40 through 42 by a conventional welding process, such as electron beam or arc welding. Alternately, a conventional friction or inertial welding process can be used to form the weld. An air-tight continuous circumferential weld is formed between the outboard end of the wheel rim and the inboard surface of the wheel disc collar.
Typically, it is difficult to weld the partial wheel rim coaxially upon the wheel disc. If the outboard and inboard tire bead seats of the assembled wheel are outside the required tolerance limits for maintaining the a coaxial relationship between the tire bead seats, undesirable vibrations may occur when the wheel is mounted upon a vehicle and the vehicle operated. Thus, it is necessary to machine the tire bead seats of the assembled wheel in functional block 48 to assure that the required amount of coaxilality is achieved.
This invention relates to a process for spin forming a portion of a vehicle wheel rim.
As described above, forming a one piece vehicle wheel involves machining a rough blank to a final shape. The sidewall formed on the outboard end of the wheel rim is typically solid due to the limitations of the casting and forging processes. While it is known to form lightener pockets in the wheel sidewall to reduce the wheel weight, the known methods typically involve complex mold or die mechanisms having retractable cores for forming the lightener pockets. The retractable cores permit removal of the casting from the mold or die. Accordingly, it would be desirable to simplify the formation of lightener pockets in the wheel sidewall to reduce the weight of the wheel.
As also described above, a two piece wheel is typically fabricated by welding a preformed wheel rim to a finished wheel disc. While forming the rim, it is difficult to achieve true circularity. Furthermore, it also is difficult to weld the rim coaxially onto the disc. Accordingly, machining is needed to true the coaxiality of the tire bead seats. Such machining is time consuming and expensive. Additionally, while the machining produces a tire bead seat having a circular outer surface, the inner surface of the rim beneath the inboard tire bead seat remains irregular. As a result, the thickness of the wheel rim beneath the inboard tire bead seat is non-uniform, causing imbalance in the wheel. Thus, it would be desirable if a two piece wheel could be fabricated which has the desired concentricity and a uniform rim thickness without the final machining of the tire bead seats.
The present invention contemplates that the wheel blank 53 remains clamped upon the mandrel 61 throughout the entire forming operation. Thus, all surfaces are formed coaxially with the axis of the mandrel 61. Additionally, because the outboard tire bead seat 22 is machined coaxial with the wheel axis 57 and the wheel blank 53 is mounted upon the mandrel with the wheel axis 57 coaxial with the mandrel axis, the inboard tire bead seat 83, which is formed coaxial with the mandrel axis, will also be formed coaxial with the outboard tire bead seat 22. The inventor expects that the tolerance of tire bead seat coaxiality which can be obtained with the above spinning operation will be better than the tolerance obtained with the prior art machining operation described above.
It is further contemplated that the process can include forming the wheel blank by attaching a hoop of metal to an inboard face of a full face wheel disc. The metal hoop is attached to the wheel disc with an air-tight continuous circumferential weld. The metal hoop can be formed by rolling a strip of metal into a hoop and butt welding the ends of the hoop together. Also, the hoop can be flared and the wheel disc heat treated before the hoop is attached to the wheel disc.
In the preferred embodiment, the wheel disc includes an annular sidewall having an outboard tire bead seat formed thereon and at least one lightener pocket formed in the sidewall extending axially beneath the outboard tire bead seat.
The invention also contemplates forming the wheel blank by securing the wheel disc within a metal hoop to form a wheel blank. The metal hoop is then spun to form a wheel rim having both inboard and outboard tire bead retaining flanges.
Alternately, the wheel blank can be cast or forged as a single piece.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.